In data storage technology, many types of storage technologies (which may also be referred to as storage solutions) exist, and provide a wide range of price, performance, capacity, and functionality. Generally, storage technologies that provide the fastest access, such as solid-state drive (SSD) technology devices and hard disk drive (HDD) technology devices, are more expensive (per unit of storage) than storage technologies that provide slower access, such as optical discs and magnetic tape drives. Thus, many data storage systems are designed and implemented with two or more tiers of storage technology, with more expensive but faster storage technology used in one or more higher tiers and less expensive but slower storage technology used in one or more lower tiers. Storage management methods (e.g., hierarchical storage management (HSM) methods) have been developed that direct the storing of data to different tiers in these data storage systems.
However, conventional storage management methods such as HSM typically consider only one dimension (access history) of information about data when making storage decisions, and typically only migrate data up or down a one-dimensional tier of data storage technologies according to the one dimension. For example, HSM methods generally store data that has been recently accessed (e.g., written or read) to the higher tier(s) (e.g., disk drives), and migrate data that has not been recently accessed (e.g., for a specified period) down to the lower tier(s) (e.g., tape). Data that has been migrated down (e.g., to tape) may be brought back up to a higher tier, generally only upon receiving an access request for the data. Data that is migrated up to a higher tier may remain on the tier for the specified period before being migrated back down to a lower tier (e.g., tape).
While embodiments are described herein by way of example for several embodiments and illustrative drawings, those skilled in the art will recognize that embodiments are not limited to the embodiments or drawings described. It should be understood, that the drawings and detailed description thereto are not intended to limit embodiments to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope as defined by the appended claims. The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims. As used throughout this application, the word “may” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include”, “including”, and “includes” mean including, but not limited to.